It is well known that the most favourable conditions for internal combustion engine operation are provided when the cylinders are fed with a homogeneous air-fuel mixture, i.e. such as mixture in which all the fuel is in a vapor phase. These conditions make it possible to accomplish a number of objects, the prinicpal ones being as follows: to increase the efficiency of fuel combustion due to a high rate and uniformity of the process of fuel burning to a complete burn-up of the fuel, to reduce the noxious exhaust gas emission, and to improve fuel economy of the engine due to the increase of the completeness of fuel combustion and of the limit of efficient leaning of the air-fuel mixture. Thus, taking into account present-day energy and ecological problems, it is readily apparent that the achievement of homogeneity of an air-fuel mixture when delivering fuel to an internal combustion engine is an important and urgent problem. The efforts of the designers of fuel systems for internal combustion engines are directed towards solving this problem.
One of the ways of solving said problem consists in providing previous vaporization of fuel in an intake duct when the fuel is supplied onto the surface of a vaporizing element. In this respect there was developed a number of devices for fuel delivery to an internal combustion engine employing both centralized fuel supply to all the engine cylinders and individual fuel injection into each engine cylinder. Some of these devices providing better understanding of the objects of the present invention as well as of the features and advantages thereof are described below.
Thus, known in the prior art is a device for fuel delivery to an internal combustion engine, comprising a vaporizing element disposed in an intake duct and made as a number of tubes on which operating surface a fuel atomized by a carburetor is continuously fed and which have a heat-transfer agent circulating therein and transferring the heat of exhaust gases due to its evaporation in a boiler and condensation on the inner walls of the tubes. The boiling point of this heat-transfer agent has a definite value sufficient for vaporization of all the fractions of a gasoline used as a fuel and provides operation of the entire operating surface of the vaporizing element at this temperature (Tony Curtis, "Meet the Vapipe," Motor, London, 1973, Vol. 143, No. 3688, p. 26-27). A limitation of the temperature in this device to a definite value considerably reduces thermal decomposition of the fuel and prevents it from autoignition in the intake duct, which may occur in devices with a vaporizing element whose operating surface has a temperature which is not adjusted and may reach undue values. However, this device cannot provide complete evaporation of all fuel fraction. This is caused by the fact that the operating surface of its vaporizing element is an isothermal one and gasoline fractions have different boiling points. Specifically, light fractions boil at temperatures of 28.degree. to 65.degree. C. and heavy ones boil at 190.degree. to 230.degree. C. When the fuel gets onto the high-temperature operating surface of the vaporizing element, the light fuel fractions instantly evaporating form a vapor cushion under a liquid fuel layer, that, on the one hand, sharply reduces heat-transfer intensity which retards evaporation of the remaining liquid fuel layer and, on the other hand, promotes detachment of liquid layer droplets by an air flow and their entrainment into the engine cylinder. Besides, when the temperature of the operating surface of the vaporizing element is maintained at a value required for vaporization of the heaviest fuel fraction, it may turn out that this temperature is too high for the light fractions and they are subjected to thermal decomposition.
Formation of a vapor cushion and thermal decomposition of all fuel fractions are eliminated in a device for fuel delivery to an internal combustion engine, in which the temperature field of the operating surface of the vaporizating element is not an isothermal one and the temperature increases from the values equal to, or even lower than, the boiling point of the light fuel fractions up to the values exceeding the boiling point of the heavy fuel fractions. This temperature rise occurs in the direction of motion of fuel continuously fed as a film through an annular slot in the wall of an intake duct (a patent application filed in the U.S., Ser. No. 83,312, Oct. 10, 1979). Due to progressive fraction-by-fraction vaporization of fuel preventing its thermal decomposition, such a design makes it possible to provide complete evaporation of all the fuel fractions and supply of a homogeneous air-fuel mixture into the engine cylinders.
However, in this device, as well as in the device considered hereinabove, fuel vaporization on the operating surface of the vaporizing element is performed with a continuous fuel supply, and this makes it impossible to provide exactly metered fuel delivery to the internal combustion engine cylinders. Indeed, these two devices are intended for use in systems of centralized fuel delivery to all the engine cylinders, but because of a phase overlap and difference in the lengths of connection pipes of an intake manifold the engine cylinders extract portions of the air-fuel mixture from the common flow thereof non-uniformly and different in fraction composition.
A U.S. Pat. No. 3,461,850, Aug. 19, 1969, discloses a device for fuel delivery to an internal combustion engine with vaporization of injected fuel metered out by injection nozzles separately to each engine cylinder. This device which is the nearest analog of the present invention comprises an intake and an exhaust duct, a vaporizing element having its one section heated by the heat of exhaust gases passing through the exhaust duct and the other section with an operating surface, disposed in the intake duct and forming a part of its wall, and an injection nozzle for fuel injection directed with its orifice onto the operating surface of the vaporizing element. The vaporizing element of this device constitutes such a part of the wall of the intake duct which in the zone of arrangement of the vaporizing element is also a part of the wall of the exhaust duct such that the heat of the exhaust gases is transferred to the operating surface of the vaporizing element through a common part of the walls of the intake and exhaust ducts thus providing efficient heating of this surface, the temperature field of the operating surface of such a vaporizing element being close to an isothermal one. The injection nozzle in the device under consideration is disposed on the diametrically opposite side of the intake duct with respect to the operating surface of the vaporizing element.
In such a device, it is impossible to provide stable and complete evaporation of all the fuel fractions in the course of engine operation because of an isothermal temperature field of the operating surface of the vaporizing element as mentioned hereinabove. In this case, the temperature of the operating surface of such a vaporizing element may vary with variations in the engine duty and may be either too low when the heavy fractions do not evaporate or too high when the fuel is subjected to thermal decomposition. Besides, fuel injection onto the operating surface of the vaporizing element through the entire suction air flow moving at a high rate may cause spraying of the fuel jet and entrainment of its droplets into the engine cylinder. The entrainment of fuel droplets into the engine cylinder is also possible because of their entry into the suction air flow after the jet of the injected fuel impinges on the operating surface of the vaporizing element at an angle close to a right one.